<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="738" name="micropaleontology" parent="861" scope="Branch of paleontology dealing with fossils too small to be seen without a microscope."/><bt><term thcode="2" code="861" name="paleontology" parent="291" scope="Study of life in past geologic time based on fossil plants and animals."/><term thcode="2" code="291" name="earth sciences" parent="1019" scope="Broad term for all science related to the study of the earth."/><term thcode="2" code="1019" name="sciences" parent="1" scope="Major educational fields, fields of study, and professional groupings within USGS."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><rt><term thcode="2" code="138" name="calcareous nannoplankton" parent="29" scope="Organisms of the kingdom Protista that normally produce coccoliths, microscopic structures of calcite (calcium carbonate), during some phase of their life cycle."/><term thcode="2" code="192" name="conodonts" parent="606" scope="Microscopic teeth of primitive, boneless, eel-like animals, similar to modern hagfish, that lived in many of the world's oceans from the Cambrian through Triassic Periods of geologic time (550 to 210 million years ago)."/><term thcode="2" code="250" name="diatoms" parent="29" scope="Microscopic, single-celled plants of the class Bacillariophyceae that have siliceous shells called frustules, and which grow in both marine and fresh water."/><term thcode="2" code="261" name="dinoflagellates" parent="29" scope="Single-celled planktonic organisms, chiefly marine, characterized by twirling motion and whip-like flagella with affinities to both plants and animals."/><term thcode="2" code="370" name="faunal and floral census (microscopic)" parent="619" scope="Records of counts of the different microscopic species in a core, soil, sediment, rock or water sample to determine geologic age or other characteristic of the sample.  Use for microscopic examinations."/><term thcode="2" code="414" name="fossils" parent="1005" scope="Recognizable remains such as bones, shells, leaves, burrows, impressions, or tracks of past life on the earth."/><term thcode="2" code="940" name="protists" parent="843" scope="Unicellular eukaryotes (organisms possessing nucleated cells) with affinities to both plants and animals. Classed in the Protista or Potoctista kingdom, they include protozoans, foraminifera, radiolarians, fungi and some algae."/></rt></descriptor>